1. Field of the Invention
This invention relates broadly to rolling mill control methods and apparatus. More particularly, this invention relates to a computer method and apparatus for controlling a rolling mill wherein there is included an operator update program for presetting and changing operating parameters. The invention may be used in a hot strip rolling mill, as will be referred to herein, or in other rolling mills for rolling sheets, plates, bars, billets, slabs and the like.
2. Description of the Prior Art
In a typical computer-controlled hot strip rolling mill, rolling schedule calculations for a finishing train are frequently initiated when a slab passes through the last roughing stand. A computer program for calculating a rolling schedule combines appropriate order data, such as grade, width, desired gage, etc., with operating data, such as slab thickness and temperature measurements, to generate computer reference setups involving a different set of roll speed and screwdown presets for each stand in the finishing train.
Presently, there are two major approaches to computing the reference setups for each mill stand. The first begins with computing a normal load distribution and presetting corresponding switches. Load distribution is then converted into percent reduction, desired roll force, roll speed and screw position presets for each stand. The second approach begins directly with computing a normal reduction pattern and after generating a schedule of speed and screw presets for each stand, a check is made to insure that an acceptable load distribution has been achieved.
When the computer is off-line, separate speed and screwdown preset thumbwheel switches provide manual controls for establishing the reference setups for each mill stand. Therefore, when using the first on-line approach to computing the reference setups, the mill operator's desk would normally include two different groups of manually operable switches, namely, the load distribution switches and the speed and screwdown preset switches for operator/computer interfacing. Whereas, when using the second on-line computing approach, only the preset switches would normally be included on the operator's desk.
Ideally, when the rolling mill control computer is on-line, the schedule calculations will proceed normally so that maximum quality and throughput of rolled product are achieved. However, as is sometimes the case, abnormal mill conditions arise which require human intervention to manually modify the computer-generated speed and screwdown reference setups. Manual changes are sometimes necessary to control the rolled product shape because of worn rolls, because of undesirable mill threading, to balance motor loads when the load distribution is undesirable, to adjust temperature of the rolled product, or occasionally to overcome false automatic control signals.
When abnormal conditions arise, the operator is first confronted with the problem of making rapid decisions concerning the schedule modifications required to avoid rolling large batches of off-specification product. He is next confronted with the problem of determining whether or not the rolling mill control system will accept operator requests for modifications to computer-generated speed and screwdown setups, and if so, by what means these operator requests will be accepted. The operator must then decide whether his requests will be implemented by a second or manual set of preset devices which were added on an operator's desk alongside of a set of load distribution switches which are utilized in computer-generated setups. Alternatively, operator requests may be implemented by a second set of preset devices located alongside of a first set normally used for manual operation. In still another arrangement, particularly in older mill installations, the operator's desk may already be overcrowded so that the addition of an extra set of controls for implementing the operator's requests may have to be placed elsewhere rather than in its logical location. Thus, at this moment of decision-making, the operator is confused and subject to considerable mental adjustments in order to overcome abnormal rolling conditions.